First, preheat the oven to 350℉.
Now, mix the butter and the sugar together. Then, add in the eggs. After, mix in the milk. In another bowl, toss in the flour, baking powder, salt and the lemon zest. Next, combine the dry and wet ingredients. Lastly, fold in the zucchini.
Pour the batter into a lined loaf pan and place into the oven. Bake fro 50-60 minutes depending on your oven until the bread is cooked all the way through.
Remove the bread from the oven and allow it to cool fully. While cooling, make the icing. After making the icing, this is the best time to pour over the bread because it will thicken and harden more with time.
After the bread is cooled, slice, serve and enjoy.